Stereodynamics of Ar–CO rotation and conformational preferences of 2-amino-3-(2,4-difluorobenzoyl)-imidazo[1,2-a]pyridine

The dynamic NMR analysis of 2, a subunit of a new class of cyclic-dependent kinase inhibitors, reveals that the compound exists as two conformational isomers, Z and E, in acetone, as a consequence of the restricted rotation about the imidazopyridine–carbonyl bond. The less hindered Z-rotamer is the most abundant conformer (85:15 Z/E at 233 K) and the free energy of activation of the interconversion is 13.2 kcal mol⁻¹. The rotamer ratio and the interconversion barrier are similar in other solvents, such as CD₃OD and CDCl₃.     

Designing new isomorphic fluorescent nucleobase analogues: the thieno[3,2-d]pyrimidine core

A convergent approach for a family of fluorescent nucleosides is described. It relies on thieno[3,2-d]pyrimidine-2,4(1H,3H)-dione that serves as a core heterocycle. This condensed pyrimidine is converted into an emissive pyrimidine nucleoside analogue by N-glycosylation and into an emissive purine nucleoside analogue by C-glycosidation at the thiophene's beta position. The design principles of this archetypical system are outlined together with the syntheses and photophysical properties of the resulting nucleosides.     

Combined spectroscopy and microscopy of supported MoS2 nanoparticles

Supported molybdenum-sulfide nanoparticles are known catalysts for petroleum hydrodesulfurization as well as for electrochemical hydrogen evolution. In this study, we investigate molybdenum-sulfide nanoparticles supported on Au(1 1 1) using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM), aiming to correlate spectroscopically determined chemical states with atomically resolved nanostructure. The results of this study allow us to conclude the following: (1) the XPS results from our model system are in good agreement with previously published results on supported MoS₂ for industrial applications, validating in part the fidelity of the model system; (2) STM reveals that catalytically active, crystalline MoS₂ nanoparticles exhibiting the well-known metallic edge state are only present after a post-deposition annealing step in the synthesis procedure, without which the particles exhibit amorphous shapes and incomplete sulfidation; and (3) the sulfided nanoparticles are found to be stable in air at room temperature.     

Homomorphisms on Function Lattices

In this paper we study real lattice homomorphisms on a unital vector lattice , where X is a completely regular space. We stress on topological properties of its structure spaces and on its representation as point evaluations. These results are applied to the lattice of real Lipschitz functions on a metric space. Using the automatic continuity of lattice homomorphisms with respect to the Lipschitz norm, we are able to derive a Banach-Stone theorem in this context. Namely, it is proved that the unital vector lattice structure of Lip (X) characterizes the Lipschitz structure of the complete metric space X. In the case of bounded Lipschitz functions, an analogous result is obtained in the class of complete quasiconvex metric spaces.     

A consensus view of the temperature dependence of the gas phase reaction: OH + HBr → H2O + Br

The temperature dependence of the rate coefficient for the reaction, OH + HBr has been reinvestigated at low temperatures (T = 48–224 K) by using uniform supersonic flow reactors with laser induced fluorescence detection. This paper presents two forms of global fits: k(T) = 1.11 × 10^?11 (T/298)^?0.91 cm³ s^?1 and k(T) = 1.06 × 10^?11 (T/298)^?1.09 cm³ s^?1, both of which accurately describe the temperature dependence of the rate coefficient for the title reaction within the temperature range 20–350 K. These fits indicate that at temperatures below 200 K, the rate coefficient for this reaction shows inverse temperature dependence, while above 200 K the reaction shows insignificant temperature dependence. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 339–344, 2002     

Size- and support-dependent electronic and catalytic properties of Au0/Au3+ nanoparticles synthesized from block copolymer micelles

Supported Au nanoclusters synthesized from diblock copolymer micelles can be reliably prepared with well-controlled sizes and dispersions. For particles with diameters between approximately 1 and 6 nm, the particle size and the support were found to strongly influence the oxygen reactivity, the formation and stabilization of a metal-oxide, and the catalytic activity for electrooxidation of carbon monoxide. The smallest particles studied (1.5 nm) were the most active for electrooxidation of CO and had the largest fraction of oxygen associated with gold at the surface as measured by the Au(3+)/Au(0) X-ray photoemission intensities. Conducting and semiconducting substrates, ITO-coated glass and TiO(2), respectively, were associated with greater stabilization of Au(3+) oxide as compared to insulating, SiO(2), substrates.     

Development of a shear char strength sensing technique to study thermoplastic polyurethane elastomer nanocomposites

Ablative materials, such as thermoplastic elastomer nanocomposites (TPUNs) are used as internal insulation materials for solid rocket motors. These TPUNs are thermoplastic elastomer reinforced by montmorillonite nanoclays, carbon nanofibers, and multi‐walled carbon nanotubes. When these TPUN materials are exposed to an extreme heat flux, a char layer forms along the surface as it ablates. This research aims to use the newly developed shear strength sensor to evaluate the shear strength of this char layer, a characteristic that is important to evaluate ablative materials. This device consists of a method to apply a transverse loading on a test specimen, while measuring the reaction force and the induced strain. This device was used on several types of TPUN test specimens to demonstrate its effectiveness. As a means to determine which ablative exhibited the best performance, the energy of destruction or the energy of dissipation was developed. The maximum force was also accounted for as a secondary quantity for determining the char shear strength. This new shear char strength sensor is fully automated to ensure that each test is repeatable. This guaranteed reliability when collecting the data and eliminated the potential for human error. Copyright © 2017 John Wiley & Sons, Ltd.     

Microscopic and macroscopic signatures of antiferromagnetic domain walls

Magnetotransport measurements on small single crystals of Cr, the elemental antiferromagnet, reveal the hysteretic thermodynamics of the domain structure. The temperature dependence of the transport coefficients is directly correlated with the real-space evolution of the domain configuration as recorded by x-ray microprobe imaging, revealing the effect of antiferromagnetic domain walls on electron transport. A single antiferromagnetic domain wall interface resistance is deduced to be of order 5 x 10(-5) mu Omega cm(2) at a temperature of 100 K.     

Evaluation of Adding Natural Gum to Pectin Extracted from Ecuadorian Citrus Peels as an Eco-Friendly Corrosion Inhibitor for Carbon Steel

The production and use of eco-friendly corrosion inhibitors allows valuable compounds contained in plant waste to be identified and repurposed while reducing the use of polluting synthetic substances. Pectin extracted from Tahiti limes (Citrus latifolia) and King mandarin (Citrus nobilis L.) in addition to natural gums—xanthan gum and latex from the “lechero” plant (Euphorbia laurifolia)—were used to create an eco-friendly corrosion inhibitor. The optimal extraction conditions for pectin were determined from different combinations of pH, temperature, and time in a 2³ factorial design and evaluated according to the obtained pectin yield. The highest pectin extraction yields (38.10% and 41.20% from King mandarin and lime, respectively) were reached at pH = 1, 85 °C, and 2 h. Extraction of pectic compounds was confirmed using Fourier-transform infrared spectroscopy, differential scanning calorimetry, and thermogravimetry analyses. Subsequently, a simplex-centroid mixture design was applied to determine the formulation of extracted pectin and natural gums that achieved the highest corrosion inhibitor effect (linear polarization and weight loss methods in NACE 1D-196 saline media using API-5LX52 carbon steel). Impedance spectroscopy analysis showed that the addition of xanthan gum to pectin (formulation 50% pectin–50% xanthan gum) improved the corrosion inhibitor effect from 29.20 to 78.21% at 400 ppm due to higher adsorption of inhibitory molecules on the metal surface.     

A Banach–Stone Theorem for Uniformly Continuous Functions

 In this note we prove that the uniformity of a complete metric space X is characterized by the vector lattice structure of the set U(X) of all uniformly continuous real functions on X.